1. Field of the Invention
Embodiments of the present invention generally relate to a process for forming crystalline solar cells.
2. Description of the Related Art
Solar cells are photovoltaic devices that convert sunlight directly into electrical power. The most common solar cell material is silicon, which is in the form of single or multicrystalline substrates, sometimes referred to as wafers. Because the amortized cost of forming silicon-based solar cells to generate electricity is higher than the cost of generating electricity using traditional methods, there has been an effort to reduce the cost required to form solar cells.
There are various approaches for fabricating the active regions and the current carrying metal lines, or conductors, of the solar cells. Manufacturing high efficiency solar cells at low cost is the key for making solar cells more competitive for the generation of electricity for mass consumption. The efficiency of solar cells is directly related to the ability of a cell to collect charges generated from absorbed photons in the various layers. A good passivation layer can provide a desired film property that reduces recombination of the electrons or holes in the solar cells and redirects electrons and charges back into the solar cells to generate photocurrent. When electrons and holes recombine, the incident solar energy is re-emitted as heat or light, thereby lowering the conversion efficiency of the solar cells.
A passivation layer disposed on a back surface of solar cell devices may be a dielectric layer providing good interface properties that reduce the recombination of the electrons and holes, drives and/or diffuses electrons and charge carriers back to junction regions formed in the substrate and minimize light absorption. Furthermore, the passivation layer disposed on the back surface of the solar cell devices may also serve as a backside reflector to minimize light absorption while assisting reflecting light back to the solar cell devices. In conventional practice, the passivation layer may be etched, drilled and/or patterned to form openings (e.g., back contact through-holes) that allow portions of the blanket back contact metal layer to extend through the passivation layer to form an electrical contact with the active regions of the device. Furthermore, conventional passivation layer processing sequences, which typically include laser ablation of the passivation layer steps, post laser processing cleaning steps, and blanket rear surface metal deposition steps, are costly, require a large number of processing steps and can create undesirable contamination that can inadvertently damage the solar cell devices.
Therefore, there exists a need for an improved method and apparatus to manufacture solar cell devices that have a desirable device performance as well as a low manufacture cost.